Sex-lethal (Sxl) is the Drosophila sex determination master switch and controls all aspects of sexual development. The functions of Sxl protein are numerous; it is a splicing and translational regulator, both fundamental biological processes that are also used for regulatory control. Recently, we have shown that the female germ line stem cells and early cystoblasts use the Hedgehog(hh) signaling pathway to regulate the trafficking of Sxl into the nucleus and its degradation. This is the first demonstration that the Hh pathway regulates a protein other than its known target, Cubitus interruptus (Ci). We also find that in all cells Sxl protein is in a complex with Fused and Costal2 proteins, the cytoplasmic components of the Hh signaling pathway. We hypothesize that the general trafficking of Sxl protein between the cytoplasm and nucleus utilizes components of the Hh signaling pathway and that this reflects a fundamental function of these proteins that is not restricted to Hh signaling. To test this hypothesis, we plan to analyze at the genetic, molecular and biochemical level the interactions of the known protein components complexed with Sxl protein. This will be done in tissue culture cells that have an intact Hh signaling system as well as whole animals. It will involve: 1). Mapping the Sxl protein nuclear import and export signals. 2). Determining the interactions between Sxl protein and the cytoplasmic Hh signaling components. 3). Analyzing the effects of genetically removing and overexpressing the different players of the Hh signaling pathway on the distribution and function of Sxl protein. 4). Examining the composition of proteins complexed with Sxl in extracts. The mutated forms of several of the components of the hedgehog pathway have been shown to give rise to tumors. The Gli protein (Ci homolog) appears to be an oncogene in humans giving rise to teratocarcinomas, liposarcomas and osteosarcomas. Many cases of basal cell carcinomas show a mutated Patched protein (the Hh receptor). Understanding the Hh signaling pathway and the different processes it regulates will be important to understanding and curing various cancers.